1. Field of the Invention
This invention relates to the field of access control devices, such as the type that are used to control vehicular traffic. More specifically, the present invention comprises a control system for actuating the opening and closure of dual swing gates.
2. Description of the Related Art
Dual swing gates are common devices used to control vehicular traffic. Dual swing gates are characterized by a pair of swing gates that move in unison. Typically, each gate blocks approximately half of the width of the access point when in the closed position. These gates are commonly used to regulate vehicular access to residences, parking garages, and industrial or commercial areas.
Most dual swing gates are electronically controlled so that an authorized vehicle is permitted to pass through the gate when the authorized vehicle approaches the gate. Various mechanisms are used to regulate the opening of the dual swing gate. Bar code scanners, card readers, infrared motion detectors, and currency counters are all commonly used to send an “open gate” command to a controller. The controller interfaces with a prime mover to open the gate when this signal is received. Motion sensors or sensors embedded in the roadway are often used to provide an “all clear” signal to the controller when the vehicle is clear of the dual swing gate. The controller is then provided with a “close gate” signal after the “all clear” signal is received.
Many dual swing gates employ locking or closing features which help secure the access point. For most locking or closing features to work properly, the swing gates must arrive at the closed position in the correct sequence. FIG. 1 illustrates the correct closure of a dual swing gate. Housing 10 and housing 20 contain motors and control devices for actuating master arm 12 and slave arm 18, respectively. In this instance, slave arm 18 reached its closure position prior to master arm 12. The correct timing allowed electronic lock device 14 to engage electronic lock receiver 16. FIG. 2 illustrates the incorrect closure of a dual swing gate. In this example, master arm 12 reached the closure position prior to slave arm 18. Because the gates closed out of sequence, electronic lock device 14 cannot engage electronic lock receiver 16.
Conventionally, this sequencing problem has been addressed by using a time delay between the movement of one gate (the “master”) and the other (the “slave”). The time delay is controlled by the circuitry of a control card that electronically actuates the movement of the master gate and the slave gate. Typically, the fixed time delay is user adjustable via DIP switch or potentiometer. A time delay of approximately four seconds is customary. When the “close gate” command is initiated, the controller first actuates closure of slave arm 18. Once the designated delay time elapses, master arm 12 is actuated. Assuming that both gates are traveling at the same speed, slave arm 18 should reach the closure point before master arm 12. This method is considered “open-loop” control.
There are many problems with this open-loop control protocol. First, the delay time may be insufficient to ensure correct sequencing if the master arm moves faster than the slave arm. Also, the relative speed of the gates may change over time due rendering the original delay time insufficient. The slave arm may have a smaller opening angle than the master arm. For example the slave arm may open to 80 degrees while the master arm opens to 100 degrees. In addition, using extended delay periods to compensate for the potential of aging can cause some to perceive that master gate has stopped working. For example, if the master arm is set to a 4 second delay period and the slave arm takes 2 seconds to close, there will be a period of 2 seconds when neither gate is moving. These control systems are not user friendly since the sequencing of the gates must be observed periodically because of the aforementioned factors which can negatively affect proper sequencing. As a result, may users tend to select the longest delay times that are possible to ensure proper closure. This increases the total time of closure and decreases the security and effectiveness of the access control system.